Volume Measuring Intervertebral Tool System and Method

ABSTRACT

The invention includes a system and method for the loosening of tissue. In one embodiment, a method of removing intervertebral tissue includes removing tissue with a loosening member to form a void, inserting a portion of the loosening member into the void, and determining the amount of tissue removed based upon the volume defined by the portion of the loosening member inserted into the void.

This application is a divisional of prior application Ser. No.11/726,954, filed Mar. 23, 2007, which is herein incorporated byreference in its entirety.

FIELD OF THE INVENTION

This invention relates to surgical devices and, more particularly, todevices used to loosen tissue for removal in a surgical patient.

BACKGROUND

The spinal column acts as a major structural support. Variousmechanisms, however, affect the ability of intervertebral disks toprovide the requisite stability and support. For example, the normalaging process tends to weaken the bones and tissues associated with thespinal column increasing the risk of spinal injuries. Additionally,sudden movements may cause a disk to rupture or herniate. A herniationof the disk is primarily a problem when the nucleus pulposus protrudesor ruptures into the spinal canal placing pressure on nerves which inturn causes spasms, tingling, numbness, and/or pain in one or more partsof the body, depending on the nerves involved. Further deterioration ofthe disk can cause the damaged disk to lose height and to produce bonespurs. These mechanisms may result in a narrowing of the spinal canaland foramen, thereby causing undesired pressure on the nerves emanatingfrom the spinal cord.

Treatments of spinal cord conditions include various procedures whichinvolve the removal of all or a portion of a spinal component. Suchprocedures may include the injection of an enzyme into an affected diskto dissolve tissues. The enzymes typically used in this procedure areprotein-digesting enzymes which must be carefully placed with respect tothe spinal defect to avoid inadvertent dissolution of spinal tissue.

Alternatively, surgical access to a spinal area may be obtained and atool such as a curette, osteotome, reamer, rasp, or drill may be used tomechanically reshape a component of the spinal column. The tissueremoved may include disk tissue which is causing pressure on a nerve orthe spinal canal. This technique is highly invasive and traumatic to thebody, and therefore requires an extended recovery period. Moreover,there are increased risks of future problems due to the removal of aportion of the lamina which is no longer in place to support and protectthe spinal canal at the area where the surgery took place.

Surgical access may also be used for spinal fusion surgery. In a fusionprocedure, a damaged disk may be completely removed. Parts of a bonefrom another part of the patient's body, such as the pelvis, areharvested, and the bone parts or grafts are subsequently placed betweenthe adjacent vertebrae so that the adjacent vertebrae grow together in asolid mass. The recovery time for a normal spinal fusion surgery issignificant due not only to the fact that normal movement cannot beallowed until detectable bone growth has occurred between the bonegrafts and the adjacent vertebrae, but also due to the fact that theassociated ligaments and muscles, both at the spinal location and thelocation where the bone grafts were harvested, must also recover.

Recently, efforts have been directed to replacing defective spinalcolumn components. When this type of procedure is performed in aminimally invasive manner, it is known for various devices implantedduring the procedure to be subsequently expelled from the intervertebraldisks. This expulsion is frequently attributed to inadequate clearanceof the nucleus during the minimally invasive surgical procedure. Theresult is that the interdiskal device extrudes from the cavity formed inthe spinal column, increasing the potential for expulsion.

A need exists for a device for loosening tissue that is minimallyinvasive, easy to use, and safe. A further need exists for a devicewhich provides for both the loosening of tissue and the removal ofloosened tissue. A further need exists for a device which can be used todetermine the amount of loosened tissue that has been removed.

SUMMARY

A system and method for loosening of tissue is disclosed. In accordancewith one embodiment according to the invention a method of removingintervertebral tissue includes removing tissue with a loosening memberto form a void, inserting a portion of the loosening member into thevoid, and determining the amount of tissue removed based upon the volumedefined by the portion of the loosening member inserted into the void.

In accordance with another embodiment, an intervertebral tissue removalsystem includes a cannula having a first end portion for insertion intotissue, a feed passage within the cannula, a return passage within thecannula, and a loosening member movable within the feed passage and thereturn passage and at least partially deployable away from the first endportion of the cannula.

In accordance with a further embodiment, a tissue loosening deviceincludes a cannula, a loosening member extending outwardly of thecannula, a moving member operably engaged with the loosening member formoving the loosening member, and a locking member movable between afirst position, wherein the locking member restricts movement of theloosening member and a second position wherein the locking member allowsmovement of the loosening member. The locking member configured suchthat when the locking member is in the first position and the looseningmember is moved by the moving member the loosening member is deployedfrom the cannula, and when the locking member is in the second positionand the loosening member is moved by the moving member the looseningmember is rotated about a loop path.

The above-described features and advantages, as well as others, willbecome more readily apparent to those of ordinary skill in the art byreference to the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a schematic view of an intervertebral tissue removalsystem with a crank handle, a clutch control, a brake lever and acannula incorporating principles of the present invention;

FIG. 2 depicts a partial cross-sectional view of a moving member, alocking member and a continuous loop loosening member within a feedpassage and return passage of the cannula of FIG. 1;

FIG. 3 depicts a partial cross-sectional view of the cannula of FIG. 1with a biasing member acting upon a tensioning member to keep theloosening member of FIG. 2 taut completely about the loop path;

FIG. 4 depicts a partial perspective view of the loosening member ofFIG. 2 showing different types of links;

FIG. 5 depicts a partial perspective view of an alternative looseningmember incorporating principles of the present invention;

FIG. 6 depicts a partial schematic view of the intervertebral tissueremoval system of FIG. 1 with the cannula positioned partially within adisc;

FIG. 7 depicts a partial schematic view of the intervertebral tissueremoval system of FIG. 1 with the cannula positioned partially within adisc which has a void formed therein;

FIG. 8 depicts a partial cross-sectional view of the cannula of FIG. 1with the locking member engaged with the loosening member;

FIG. 9 depicts a partial schematic view of the intervertebral tissueremoval system of FIG. 1 with the cannula positioned partially within adisc with a portion of the loosening member deployed from the cannula tomeasure the volume of the void formed in the disc;

FIG. 10 depicts a partial cross-sectional view of an alternativeembodiment of a cannula with aspiration branches provided through theloosening track of the cannula in accordance with principles of thepresent invention;

FIG. 11 depicts a partial cross-sectional view of an alternativeembodiment of a cannula with a biasing member that is located outside ofthe loop path and which biases a tensioning track away from a looseningtrack in accordance with principles of the present invention;

FIG. 12 depicts a partial cross-sectional view of an alternativeembodiment of a cannula with a loop path formed by a freewheeling memberand a moving member;

FIG. 13 depicts a partial plan view of an alternative embodiment of acannula including a steerable tip portion in accordance with principlesof the invention;

FIG. 14 depicts a partial cross-sectional view of the cannula of FIG. 13showing the use of spacers to influence the path of a loosening member;

FIG. 15 depicts a cross-sectional view of the steerable tip portion ofthe cannula of FIG. 13 looking from the pivot pin toward the pivot andshowing indentations on the spacer members that are used to influencethe path of the loosening member;

FIG. 16 depicts a side perspective view of an alternative intervertebraltissue removal device with a crank handle, a clutch control, a brakelever and a cannula with a pivoting tip incorporating principles of thepresent invention;

FIG. 17 depicts a side perspective view of the tissue removal device ofFIG. 16 with the pivoting tip of the canula pivoted with respect to theposition of the pivoting tip in FIG. 16;

FIG. 18 depicts a partial side cross-sectional view of the pivoting tipof the device of FIG. 16 with a perspective view of the loosening membershowing the loosening member extending within passages in the cannulaand around a bearing with a diameter larger than the width of thedivider between the passages;

FIG. 19 depicts a partial side cross-sectional view of an alternativetissue removal device with a perspective view of a loosening membershowing the loosening member extending within passages in the cannulaincorporating principles of the present invention;

FIG. 20 depicts a partial end cross-sectional view of the tissue removaldevice of FIG. 19 with a perspective view of the loosening membershowing the footprint of the loosening member within the cross-sectionsof the passages; and

FIG. 21 depicts a partial end cross-sectional view of an alternativetissue removal device with a perspective view of the loosening membershowing the footprint of the loosening member within the shapedcross-sections of the passages.

DETAILED DESCRIPTION

FIG. 1 depicts an intervertebral tissue loosening device 100 whichincludes a grip 102, a main housing 104 and cannula 106. A crank handle108, a clutch 110 and a brake lever 112 extend from the main housing104. An aspiration port 114 and an outlet port 116 are provided on thecannula 106. The cannula 106 preferably has a diameter of between about3 millimeters to about 10 millimeters.

A fluid reservoir 118 is in fluid connection with the cannula 106through a tube 120 which is connected to the aspiration port 114. Inthis embodiment, the fluid reservoir 118 is configured to provide aliquid in the form of saline solution under pressure to the aspirationport 114. The fluid may be pressurized in a number of acceptable wayssuch as using a gas to pressurize the fluid reservoir 118 or a pump thattakes suction from the fluid reservoir 118.

The outlet port 116 is in fluid connection with a collector 122 througha tube 124. In alternative embodiments, the collector 122 may bereplaced with a vacuum collection system so as to provide a suctionsource for the cannula 106 through the outlet port 116. Additionally,the tube 124 may be directed to waste if so desired.

The crank handle 108 is operably connected to a belt 126 which extendsinto the cannula 106 as best seen in FIG. 2. The belt 126 is operablyconnected to a sprocket 128 which is rotatably mounted on a pin 130. Thesprocket 128 is engaged with a chain 132 formed in a continuous loopwhich extends along a feed passage 134, a loosening track 135 and areturn passage 136 of the cannula 106. The chain 132 preferably has adiameter in the range of about 1 millimeter to about 3 millimeters. Alsoshown in FIG. 2 is a locking member 138 which is pivotably mounted tothe cannula 106 by a pin 140. A connector arm 142 is pivotably connectedto the locking member 138 and operably connected to the brake lever 112.

Continuing with FIG. 3, the chain 132 extends around a tensioningportion 144 that is located within the cannula 106. The tensioningportion 144 includes a blind bore 146 which receives a biasing member148. The biasing member 148, which is configured to provide a relativelyconstant biasing force as it is compressed, is maintained within theblind bore 146 by a stop 150 which is fixedly connected to the cannula106. A tube 152 is in fluid communication with the aspiration port 114at one end.

The other end of the tube 152 is in fluid communication with anevacuation chamber 156 through an opening 154 in a tensioning track 155of the tensioning portion 144. The evacuation chamber 156 is in fluidcommunication with the outlet port 116. An indicator 158 is connected tothe tensioning portion 144 and is visible through a sight glass 160shown in FIG. 1. A plurality of gradations 162 are located on thecannula 106 adjacent to the sight glass 160.

The chain 132 is made from a plurality of loosening links 164 andconnecting links 166 shown in FIG. 4. The loosening links 164 include aloosening edge 168 which extends above the other portions of theloosening links 164 and the connecting links 166 as seen best in FIG. 2.The loosening links 164 and the connecting links 164 define voids 170and 172, respectively. A variety of chain configurations may be used inan apparatus incorporating principles of the present invention. By wayof example, the chain 174 shown in FIG. 5 includes a plurality of links176. Each of the links 176 are identical and include a loosening edge178 and a void 180. The loosening edges 178 are formed in the links 176by twisting the links 176 such that the loosening edges 178 extend abovethe plane in which the remaining portions of the links 170 are located.Alternatively, the chain may be fashioned such that the loosening edgesare generally within the plane of the adjacent links and only extendoutwardly as the chain is rotated about a pivot.

In operation, a surgical site is prepared in an acceptable manner andthe cannula 106 is used to puncture a disc 182 as shown in FIG. 6. Inthis example, aspiration is to be used to assist in the removal oftissue. Accordingly, the tube 120 is connected to the aspiration port114 and the tube 124 is connected between the outlet port 116 and thecollector 122. Alternatively, the tube 124 may be connected to a drainor a vacuum device. Of course, the foregoing steps may be accomplishedin a number of alternative variations. For example, the fluid supplycomponents and outlet components may be connected prior to insertion ofthe cannula 106 into the disc 182.

Once the canula 106 is positioned in the disc 182, pressurized fluid isintroduced into the tube 120. This may be accomplished by pressurizingthe fluid reservoir 118 such that pressurized fluid is directed throughthe tube 120 and the aspiration port 114 into the tube 152. The crankhandle 108 is then rotated in the clockwise direction as indicated bythe arrow 184 in FIG. 6. Such rotation of the crank handle 108 causesthe belt 126 to rotate in the direction of the arrows 186 in FIG. 2causing the sprocket 128 to rotate in the direction of the arrow 188about the pin 130.

As the sprocket 128 rotates, the arms of the sprocket 128 extend intothe voids 170 and 172 of the loosening links 164 and the connectinglinks 166, respectively. The biasing member 148 acts upon the tensioningportion 144 thereby maintaining the chain 132 in a taut conditionbetween the tensioning track 155 and the loosening track 135.Accordingly, the rotation of the sprocket 128 forces the chain to rotatethrough the feed passage 134 over the loosening track 135, through thereturn passage 136 and over the tensioning track 155 in the direction ofthe arrow 190. In alternative embodiments, a friction wheel may be usedin place of a sprocket.

As the chain 132 moves in the direction of the arrow 190, the looseningedges 168 of the loosening links 166 extend into the disc 182 as theloosening track 135 presses the chain 132 into the disc 182. Theloosening edges 168 thus loosen tissue within the disc 182, forming avoid 192 within the disc 182 as shown in FIG. 7. If desired, the clutch110 may be adjusted such that rotation of the crank handle 108 causesrotation of the chain 132 so long as the chain 132 is engaging tissuewithin the disc 182. If the chain 132 encounters a harder material,however, the increased torque will exceed the clutch setting and thesprocket 128 will no longer rotate. The clutch 110 may thus be used toreduce the potential of inadvertently damaging the surroundingvertebrae.

The loosened tissue is entrained within the voids 170 and 172 and by theloosening edges 168 and moved out of the disc 182 into the returnpassage 136. As the voids 170 and 172 and the loosening edges 168 rotatepast the opening 154 in the tensioning track 155, the fluid passingthrough the tube 152 dislodges the entrained tissue out of the voids 170and 172 and the loosening edges 168. The fluid and the dislodged tissuepasses into the evacuation chamber 156 and exit the cannula 106 throughthe outlet port 116. The tube 124 then directs the fluid and thedislodged tissue to the collector 122.

The size of the void 192 formed in the disc 182 may be determined bycomparing the volume of the fluid from the fluid reservoir 118 beforeand after loosening of tissue with the volume of fluid and tissue in thecollector 122. Such a determination, however, may include inaccuraciesdue to leakage of the fluid, entrapment of fluid and/or tissue withinthe evacuation chamber 156, and other errors. Moreover, the volume oftissue and fluid in the collector 122 does not provide information as tothe shape of the void 192. Accordingly, in one method, the tissueloosening device 100 is used to determine the volume and shape of thevoid 192.

Determination of the volume of the void 192 using the tissue looseningdevice 100 is accomplished by stopping rotation of the crank handle 108.The tissue loosening device 100 is thus in the condition depicted inFIG. 7. Specifically, the cannula 106 is located partially within thevoid 192. Additionally, the chain 132 is maintained in a full loop asdepicted in FIG. 3 by the force exerted on the tensioning portion 144 bythe biasing member 148. Thus, the indicator 158 is at the zero positionof the sight glass 160.

The brake lever 112 is then moved in the direction of the arrow 194 inFIG. 7. This causes the connector arm 142 to move in the direction ofthe arrow 196 in FIG. 2. As the connector arm 142 moves, the lockingmember 138 is pivoted about the pin 140 in the direction of the arrow198. This pivoting moves the locking member 138 from an unlockedposition to a locked position as shown in FIG. 8 wherein the lockingmember 138 extends through a void 170 in a loosening link 164.

Movement of the chain 132 into the return passage 136 is thus precludedby the locking member 138. Moreover, movement of the chain 132 along thereturn passage 136 is precluded. Next, the clutch 110 is set to ameasurement position wherein the torque required to activate the clutchis greater than the force exerted by the biasing member 148 against thetensioning portion 144. Then, the crank handle 108 is once again rotatedin the direction of the arrow 184.

The tissue loosening device 100 is then operated in a manner similar tothe tissue loosening operation described above. At this point, however,the chain 132 cannot move along the return passage 136. Accordingly, asthe force applied to the chain 132 by the sprocket 128 increases abovethe force exerted by the biasing member 148 on the tensioning portion144, the chain 132 presses against the tensioning track 155 and forcesthe tensioning portion 144 against the biasing member 148, therebycompressing the biasing member 148 and the tensioning portion 144 movesin the direction of the arrow 200 of FIG. 3.

Movement of the tensioning portion 144 in the direction of the arrow200, thus shortening the chain travel path, allows the sprocket 128 torotate in the direction of the arrow 188, thereby moving the chain 132out of the feed passage 134. Because the movement of the chain 132 intothe return passage 136 is constrained by the locking member 138, thechain 132 is not maintained in a taut condition across the looseningtrack 135. Accordingly, the chain 132 is deployed away from theloosening track 135 and deposited into the void 192.

Rotation of the crank handle 108, and thus deposition of the chain 132within the void 192, continues until the void 192 is filled with thechain 132 as depicted in FIG. 9. When the void 192 is filled, the torqueon the sprocket 128 increases rapidly. The increased torque may bedetected by the operator. Alternatively, the clutch 110 may be set todisengage the sprocket 128 when the torque on the sprocket reaches apredetermined value above the force required to compress the biasingmember 148. Thus, the disengagement of the sprocket may be used tosignal an operator that the void 192 is filled.

Because deposition of the chain 132 requires movement of the tensioningportion 144, the movement of the tensioning portion 144 may becorrelated to the amount of the chain 132 deposited into the void 192.The extent of the movement of the tensioning portion 144 may bedetermined by observing the position of the indicator 158 through thesight glass 160. The operator may further verify that the increasedtorque on the sprocket has not been caused by the full compression ofthe biasing member 148 against the stop 150.

The correlation of the amount of chain deposited within the void 192with the movement of the tensioning portion 144 may be established byinitially depositing the chain 132 into a graduated flask partiallyfilled with liquid. The displacement of the liquid within the flask bythe chain 132 may then be correlated to the position of the indicator158 with respect to the gradations 162.

If desired, the chain 132 deposited within the void 192 may further beused to ascertain the shape of the void 192. Specifically, byconstructing the chain 132 of a radiopaque material, a radiograph of thedisc 182 with the void 192 filled with the chain 132 may be used todetermine the shape of the void 192. To facilitate procedures whichrequire the chain 132 to remain in the void 192 for extended periods, alatch (not shown) or other mechanism may be provided to lock the crankhandle 108. Thus, the operator need not provide constant pressure on thecrank handle 108 to counter the force exerted by the biasing member 148.Likewise, a latch (not shown) or other mechanism may be provided tosecure the brake lever 112 in the locked position.

If the operator determines that additional tissue should be removed asthe chain 132 is withdrawn into the cannula 106, the clutch 110 may beadjusted to allow for increased torque to be exerted on the sprocket128. As the torque on the sprocket 128 increases, the chain 132 ispressed into the tissue defining the void 192 loosening additionaltissue and the loosened tissue becomes entrained in the voids 170 and172.

Once the chain 132 is no longer needed within the void 192, the chain132 is withdrawn into the cannula 106. This is preferably achieved byrotating the crank handle 108 in a direction opposite to the directionindicated by the arrow 184, thereby reversing the above describedprocess. In this manner, a controlled removal of the chain 132 isaccomplished. Once the tensioning portion 144 has moved back to itsoriginal position and the chain 132 is in the tissue removal conditionshown in FIG. 3, the brake lever 112 is moved in the direction of thearrow 202 of FIG. 9. This causes the locking member 138 to disengagefrom the chain 132, allowing additional loosening of tissue within thedisc 182 by rotation of the sprocket 128 in the manner described above.

If desired, the locking member 138 may be disengaged prior to moving thetensioning portion 144 to its original position. This allows the biasingmember 148 to force the tensioning portion 144 in the direction oppositeto the arrow 200 in FIG. 3, thereby pulling the chain 132 out of thevoid 192. The rate of removal of the chain 132 may thus be establishedby the amount of force exerted on the tensioning portion 144 by thebiasing member 148.

In either event, the sprocket 128 may be rotated such that all of thevoids 170 and 172 that were within the void 192 are directed over theopening 154, allowing aspiration fluid from the tube 152 to dislodge anyloosened tissue within the voids 170 and 172. In some procedures, oncethe desired amount of tissue has been removed, some or all of theremoved tissue is subjected to a procedure such as a test or treatment.The removed tissue may then be re-inserted into the void.

A number of tissue loosening systems may be used in accordance withprinciples of the present invention. In alternative embodiments, theshape of the loosening track is modified to provide, for example, wideror narrower loosening areas. In further alternative embodiments,movement of the chain may be controlled using a motor which drives asprocket or other device configured to engage a chain. The motor may beexternally powered or battery powered. In some embodiments, thedisplacement of liquid may be determined based upon the number ofrotations of the crank. Accordingly, after the locking member isengaged, the operator merely counts the revolutions of the crank. Inmotorized embodiments, the number of rotations may be electronicallydetermined.

FIG. 10 depicts a portion of an alternative tissue loosening device 210.The tissue loosening device 210 is similar to the tissue looseningdevice 100 and includes a sprocket 212 which drives a chain 214. Themain differences are that the tissue loosening device 210 includes anevacuation tube 216 and two aspiration branches 218 and 220 which are influid communication with an aspiration fluid supply tube 222.

In operation, a fluid supply is connected to the aspiration fluid supplytube 222. Thus, as the sprocket 212 rotates the chain 214, the chain 214loosens tissue. The aspiration fluid is passed from the aspiration fluidsupply tube 222 to the aspiration branches 218 and 220 and through thechain 214. Thus, as the chain 214 loosens tissue, the aspiration fluidpassing through the aspiration branches 218 and 220 dislodges theloosened tissue from the chain 314 and the loosened tissue andaspiration fluid is directed to the evacuation tube 216. If desired, thetissue loosening device 210 may further include a tube (not shown)within the cannula 224 similar to the tube 152 for dislodging anyloosened tissue which is not dislodged by the aspiration branches 218and 220.

A variety of configurations may be used in practicing the presentinvention. By way of example, a cannula 224 depicted in FIG. 11 houses aloosening member 226 that extends about a loop path including a feedpassage 228, a return passage 230, a loosening track 232 and atensioning track 234. The tensioning track 234 is movable with respectto the loosening track 232 and is biased away from the loosening track232 by a biasing member 236 which is fixedly connected at one end to apost 238 which is, in turn, fixedly connected to the cannula 224. Thebiasing member 236 in this embodiment is not located within the looppath. Thus, force must be used to expand the biasing member 236 whendeployment of the loosening member 226 from the cannula 226 is desired.

Another configuration is depicted in the embodiment of FIG. 12 whereinthe tissue loosening device 240 includes a cannula 242, a looseningmember 244, a moving member 246, a freewheeling member 248 and a lockingarm 250. The moving member 246 and the cannula 242 define a feed passage252 while the freewheeling member 248 and the cannula 242 define areturn passage 254. A belt 256 is used to rotate the moving member 246about a pin 258. The freewheeling member 248 is rotated about a pin 260by the loosening member 244.

Rotation of the loosening member 244 may be accomplished in the samemanner as described with respect to the chain 132 of the embodiment ofFIG. 1. The tissue loosening device 240 differs from the tissueloosening device 100 of FIG. 1 in that the loop path for the looseningmember 244 is not defined by a loosening track which underlies theloosening member 244. Rather, the positioning of the moving member 246and the freewheeling member 248 defines the shape of the loop path.Thus, various cutting widths and shapes may be provided by selection ofthe relative sizes and positions of the moving member 246 and thefree-wheeling member 248. Additionally, in the embodiment of FIG. 12 theloosening member 244 is engaged by the locking arm 250 through thefree-wheeling member 248.

FIG. 13 depicts an embodiment of a loosening device which includes apivoting cannula 262. The cannula 262 includes a base portion 264 and apivoting tip portion 266. A loosening member 268 extends outwardly ofthe pivoting tip portion 266. A positioning member 270 extends throughan eyelet 272 on the base portion 264 and is attached to a post 274 onthe pivoting tip portion 266. A second positioning member 276 extendsthrough an eyelet 278 on the base portion 264 and is attached to a post280 on the pivoting tip portion 266. In the position shown in FIG. 13,the positioning member 276 is in contact with a pivot 282.

The angle of the pivoting tip portion 266 with respect to the baseportion 264 is controlled by the tension applied to the positioningmembers 270 and 276. Specifically, by loosening the tension on thepositioning member 270 and applying increased tension on the positioningmember 276, the pivoting tip portion 266 rotates about the pivot 282 inthe direction of the arrow 284. Alternative methods may be used toposition the tip portion of a cannula including other mechanicalconstructs either on the outer surface of the cannula or constructslocated within the cannula, and the use of shape memory metals.Additionally, a cannula may incorporate more than one pivoting portionand more than one method of controlling the pivoting of the pivotingportions.

In the embodiment of FIG. 13, the loop path of the loosening member 268is defined in part by a spacer member 286 within the base portion 264,two spacer members 288 and 290 located within the pivoting tip portion266 and an end bearing 292 which in this embodiment is a pin. The spacermembers 286, 288 and 290 are used to minimize interference with themovement of the loosening member 268 from either the pivot 282 or thewalls of the pivoting tip portion 266. The spacer members 286, 288 and290 are further configured to guide the loosening member 268 so as toavoid contact of the loosening member 268 with itself as the looseningmember is loosening tissue. By way of example, the spacer members 288and 290 include grooves 294 and 296. When the loosening member 268 isplaced under tension, the groove 296 urges the outgoing portion 298downwardly within the pivoting tip portion 166 and the groove 294 urgesa return portion 300 of the loosening member 268 upwardly as shown inFIG. 15.

In this embodiment, the loosening member 268 may be in the form of asegment of chain. The loosening member 268 may be provided in the formof a long length of chain. Accordingly, a segment of the chain isobtained from the supplied chain for a particular procedure andthereafter, the used segment of chain may be discarded.

In contrast to some embodiments, the embodiment of FIG. 13 does notinclude a sprocket or friction wheel located near the pivoting tipportion 266. Rather, the loosening member 268 is manually manipulatedfrom the rear portion of the cannula 262.

The loosening member 268 may be used to loosen tissue by pulling firston the return portion 300 and then reversing the direction of theloosening member 268 by pulling on the portion 298. Thus, the portion300 becomes the outgoing portion and the portion 298 becomes the returnportion. Additionally, the embodiment of FIG. 13 does not include alocking member. Nonetheless, the loosening member 268 may be depositedwithin a void by holding one of the portions 298 or 300 and pushing onthe other of the portion 298 or 300.

FIG. 16 depicts an embodiment of a loosening device 310. The looseningdevice 310 includes a handle 312, a crank 314 and a cannula 316. A brakeactivator 318 extends outwardly from the handle 312. The cannula 316includes a pivoting tip 320 and an aspiration port 322. The pivoting tip320 is pivoted about a pivot 324 by a steering mechanism which includesa tensioning member 326 shown in FIG. 17. A loosening member 328 extendswithin the cannula 316 and outwardly from a bearing 330.

With reference to FIG. 18, two passages 332 and 334 within the cannula316 are separated by a divider 336. The passages 332 and 334 areconfigured to complement the geometry of the individual links 338 of theloosening member 328. Thus, the loosening member 328 is maintained in areduced profile within the passages 332 and 334. This configurationreduces the error in determining the volume of a void since the changein volume of the loosening member 328 within the passages 332 and 324,and particularly within the passage 332 when a locking mechanism is usedto restrict movement of the loosening member 328 within the passage 324,is reduced. Thus, more accurate determination and compensation of theerror in measurement caused by the change of volume of the looseningmember within the passages 332 and 334 is possible.

In the embodiment of FIG. 18, the bearing 330 has a cross section thatis larger than the width of the divider 336. Accordingly, as the links338 approach the end of the pivoting tip 320, the links are forcedoutwardly, away from the longitudinal axis of the passage 332. Thisallows the loosening member 328 to loosen an area of tissue that iswider than the diameter of the cannula 316. Accordingly, the looseningmember 328 may be used to provide aggressive loosening of tissue.Moreover, as shown in FIG. 18, there is a substantial amount of freearea within the links 338 of the loosening member 328, providing a largecarrying capacity for the removal of loosened tissue (T).

FIG. 19 shows a loosening member 340 within a passage 342 of a cannula344. The loosening member 340 includes a number of links 346 withcutting edges 348. The diameter of the links 346 is closely matched withthe diameter of the passage 342 as best shown in FIG. 20 which furtherdepicts a passage 350.

The links 346 are configured in this embodiment to provide a reducedamount of loosening as the edges 348 are not as pronounced as the edgesof the links 338 of FIG. 18. Additionally, there is less free areawithin the links 346 as evident by comparison of the links 338 in FIG.18 with the links 346 in FIG. 19. Thus, the loosening member 340 has amore limited carrying capacity. The lack of free area also reduces theamount of “play” in the loosening member 340. Accordingly, the looseningmember 340 may be preferred in embodiments wherein the loosening memberwill be pushed into a passage.

The configuration of FIG. 19 allows the loosening member 340 to rotatewithin the passages 350 and 342. The configuration shown in FIG. 21 maybe used to control the manner in which a loosening member is presentedto tissue to be loosened.

Specifically, the cannula 352 includes two shaped passages 354 and 356.A loosening member 358 extends within the passages 354 and 356. Thecross section of the passages 354 and 356 is complimentary to thefootprint of the loosening member 358 within the passages 354 and 356.

Accordingly, the loosening member 358 is not free to rotate within thepassages 352 or 354. Thus, the aspect of the loosening member 358 whichis presented to tissue to be loosened is controlled by the shape of thepassages 354 and 356 and the manner in which the loosening member isinserted into the passages 354 and 356. Therefore, the loosening member358 may be controlled to remain in a constant orientation.

Alternatively, the loosening member 358 may be controlled to make one ormore full rotations by twisting the loosening member 358 after theloosening member 358 exits the passage 354 and before the looseningmember 358 is inserted into the passage 356. Rotation in less than fullincrements may be accomplished by rotating the orientation of one of thepassages with respect to the other passage. Thus, various combinationsof passage geometries, such as round, rectangular and triangular andloosening member geometries including round, rectangular and triangularmay be used to provide varying degrees of control over the manner inwhich a particular loosening member functions.

While the present invention has been illustrated by the description ofexemplary processes and system components, and while the variousprocesses and components have been described in considerable detail,applicant does not intend to restrict or in any way limit the scope ofthe appended claims to such detail. Additional advantages andmodifications will also readily appear to those ordinarily skilled inthe art. The invention in its broadest aspects is therefore not limitedto the specific details, implementations, or illustrative examples shownand described. Accordingly, departures may be made from such detailswithout departing from the spirit or scope of applicant's generalinventive concept.

We claim:
 1. A method of removing intervertebral tissue comprising:removing tissue with a loosening member to form a void; inserting aportion of the loosening member into the void; and determining theamount of tissue removed based upon the volume defined by the portion ofthe loosening member inserted into the void.
 2. The method of claim 1,wherein inserting a portion of the loosening member into the voidcomprises: shortening the travel path of the loosening member.
 3. Themethod of claim 2, wherein inserting a portion of the loosening memberinto the void comprises: restricting movement of the loosening memberout of the void.
 4. The method of claim 3, wherein restricting movementof the loosening member comprises: engaging a link of a chain with alocking member.
 5. The method of claim 1, wherein removing tissue with aloosening member to form a void comprises: rotating a continuous loop ofchain links through the tissue; and loosening the tissue with aloosening edge located on at least one of the chain links.
 6. The methodof claim 5, wherein removing tissue with a loosening member to form avoid comprises: entraining the loosened tissue with the chain links;transporting the loosened tissue into a cannula with the chain links;and dislodging the loosened tissue from the chain links within thecannula.
 7. The method of claim 1, wherein removing tissue with aloosening member to form a void comprises: rotating a segment of chainlinks through the tissue in a first direction; loosening the tissue witha loosening edge located on a first at least one of the chain links; androtating the segment of chain links through the tissue in a seconddirection.
 8. The method of claim 1, wherein: inserting a portion of theloosening member into the void includes engaging a continuous loop ofchain link with a sprocket, and rotating the sprocket; and determiningthe amount of tissue removed includes determining the change in a looppath of the loop of chain link.
 9. The method of claim 1, whereindetermining the amount of tissue removed includes: determining theamount of chain link fed into a cannula.
 10. The method of claim 1wherein: inserting a portion of the loosening member into the voidincludes engaging a continuous loop of chain link with a sprocket, androtating the sprocket; and determining the amount of tissue removedincludes determining the rotation of the sprocket.
 11. The method ofclaim 1, further comprising: collecting the removed tissue; performing aprocedure on the removed tissue; and depositing the collected tissue inthe void.
 12. The method of claim 1, wherein removing tissue comprisesinserting a first portion of a cannula through an incision; inserting asecond portion of the cannula through an incision; and changing theposition of the first portion of the cannula with respect to the secondportion of the cannula.